Selective determination of tryptophan-containing peptides through precolumn derivatization and liquid chromatography using intramolecular fluorescence resonance energy transfer detection.

A selective and sensitive fluorometric determination method for native fluorescent peptides has been developed. This method is based on intramolecular fluorescence resonance energy transfer (FRET) detection in a liquid chromatography (LC) system following precolumn derivatization of the amino groups of tryptophan (Trp)-containing peptides. In this detection process, we monitored the FRET from the native fluorescent Trp moieties (donor) to the derivatized fluorophore (acceptor). From a screening study involving 10 fluorescent reagents, we found that o-phthalaldehyde (OPA) generated FRET most effectively. The OPA derivatives of the native fluorescent peptides emitted OPA fluorescence (445 nm) through an intramolecular FRET process when they were excited at the excitation maximum wavelength of the Trp-containing peptides (280 nm). The generation of FRET was confirmed through comparison with the analysis of a non-fluorescent peptide (C-reactive protein fragment (77 - 82)) performed using LC and a three-dimensional fluorescence detection system. We were able to separate the OPA derivatives of the Trp-containing peptides when performing LC on a reversed-phase column. The detection limits (signal-to-noise ratio = 3) for the Trp-containing peptides, at a 20-microL injection volume, were 41 - 180 fmol. The sensitivity of the intramolecular FRET-forming derivatization method is higher than that of the system that takes advantage of the conventional detection of OPA derivatives. Moreover, native non-fluorescent amines and peptides in the sample monitored at FRET detection are weaker than those of conventional fluorescence detection.     

Analysis of XGM-Based Wavelength-Conversion in SOAs Using Assist Light

Wavelength conversion based on the cross-gain modulation (XGM) in a traveling-wave type semiconductor optical amplifier (TW-SOA) using assist light is theoretically studied. Taking into account the spatial and temporal variations of carrier density along the SOA length, the dependency of the conversion response on the assist light conditions is simulated both for co- and counter-propagating assist light schemes.     

Preparation of poly(4-vinyl-2-hydroxypyridine) and its catalytic activity on mutarotation of 2,3,4,6-tetramethyl-α-D-glucose

Poly(4-vinyl-2-hydroxypyridine), PVHP, was prepared by the reaction of poly(4-vinylpyridine) with hydrogen peroxide in acetic acid, and subsequent refluxing in acetic anhydride at 150°C. Conversion of pyridine units to 2-hydroxypyridine units was about 75% and the obtained product was a deep-brown powder. Mutarotation rates of 2,3,4,6-tetramethyl-α-D -glucose, TMG, in chloroform and in ethanol in the presence of the PVHP were measured and compared with those in the presence of 2-hydroxypyridine. The PVHP was found to show higher catalytic activities on the mutarotation than 2-hydroxypyridine in both solvents, which was deduced to be due to more efficient formation of the complex between TMG and the catalyst molecules. The mutarotation rates were higher in chloroform than in ethanol for both catalysts, which suggests that the mutarotation in the presence of the catalyst is more favorable in the strongly hydrogen bonding solvent because of higher interaction between the substrate and the catalyst molecules. The mutarotation rates increased proportionally with increasing concentration of the substrate in both solvents and in the presence of both catalyst, while they increased but not proportionally with increasing concentration of the catalyst; the increase began to level-off with increasing concentration of the catalyst. The latter tendency was assumed to result from the association of the catalyst units themselves, which makes efficiency of the complex formation between TMG and the catalyst molecules lower. © 1993 John Wiley & Sons, Inc.     

Sequential assembly strategy for tetrasubstituted olefin synthesis using vinyl 2-pyrimidyl sulfide as a platform

We have developed a programmable and diversity-oriented synthetic scheme for tetrasubstituted olefins through a site-selective and sequential assembly of pi-components onto a C=C core of vinyl 2-pyrimidyl sulfide. Noteworthy features are that (i) all components assembled stem from readily available organic halides or their Grignard reagents, (ii) the installation at the desired position can be achieved by the addition of the components in the appropriate order, and (iii) simple alteration of addition order in the sequence results in the production of all possible regio- and stereoisomers of multisubstituted olefins.     

A general and straightforward route toward diarylmethanes. Integrated cross-coupling reactions using (2-pyridyl)silylmethylstannane as an air-stable,storable, and versatile coupling platform

[reaction: see text] Pharmacologically important diarylmethane structures have been prepared in a straightforward manner through sequentially integrated Pd-catalyzed cross-coupling reactions. (2-Pyridyl)silylmethylstannane was found to be an air-stable, storable, and versatile coupling platform in this synthetic strategy.     

Decarbonylative C-h coupling of azoles and aryl esters: unprecedented nickel catalysis and application to the synthesis of muscoride a

A nickel-catalyzed decarbonylative C-H biaryl coupling of azoles and aryl esters is described. The newly developed catalytic system does not require the use of expensive metal catalysts or silver- or copper-based stoichiometric oxidants. We have successfully applied this new C-H arylation reaction to a convergent formal synthesis of muscoride A.     

Pd(OAc)2/o-chloranil/M(OTf)n: a catalyst for the direct C-H arylation of polycyclic aromatic hydrocarbons with boryl-, silyl-, and unfunctionalized arenes

Pd(OAc)(2)/o-chloranil/M(OTf)(n) can effectively promote the C-H arylation of fluoranthene with arylboron compounds or arylsilanes. The reaction takes place with high regioselectivity at the C3 position of fluoranthene. Moreover, the new catalytic system allows the use of unfunctionalized arenes as coupling partners in the arylation of polycyclic aromatic hydrocarbons.     

Determination of Histamine in Rat Plasma and Tissue Extracts by Intramolecular Excimer-Forming Derivatization and LC with Fluorescence Detection

A highly sensitive and selective method for determination of histamine in rat plasma and tissue extracts by liquid chromatography with fluorescence detection is described. The method is based on precolumn derivatization of amino groups of histamine with two molecules of 4-(1-pyrene)butyric acid N-hydroxysuccinimide ester that allows generation of intramolecular excimer fluorescence. The detection limit for histamine was 0.183 nM. This sensitivity allowed determination of histamine in 10 μL of rat plasma or in the extracts from less than 1 mg of tissue.